Field of the Invention
The invention relates to an apparatus for conveying sheets in a printing press having at least one conveyor element for a sheet along a conveying path and at least one guide element for the sheet in the conveying direction.
In printing presses, it is known to convey sheets from the last printing unit onto a stack, the leading edge of the sheets being held on grippers that are fastened on a circulating chain mechanism. Before a sheet is deposited onto the stack, its conveying speed is reduced using braking modules that have suction belts that are narrow with regard to the sheet width. Thin sheets tend to sag between the braking modules. The sagging impairs the formation of stacks and can cause the corners to be folded over. The braking modules can be adjusted laterally to adapt the position transversely with respect to the conveying direction to the sheet width. The spacing between the braking modules can be of varying size. Therefore, the width of support elements that are provided to reduce the sagging between the braking modules must be adjustable.
German Published, Non-Prosecuted Patent Application DE 101 34 836 A1, corresponding to U.S. Pat. No. 6,557,468 to Kelm et al., describes a delivery for a sheet-fed printing press in which a plurality of braking devices are provided that can be adjusted transversely with respect to the sheet conveying direction. A sheet-guiding device including a belt of flexible material is disposed in the intermediate space between adjacent braking devices, it being possible to adapt the length of the belt transversely with respect to the conveying direction to the spacing of adjacent braking devices. Support of this type of a sheet using a roller blind is complicated in constructional terms because of the requirement for a roller blind tensioning mechanism and requires a large amount of installation space. In addition, the deflection and tensioning rollers used are sensitive to contamination, in particular, in deliveries in which the sheets are powdered to prevent smudging.
Furthermore, guide plates or guide loops are known as support elements, in which no measures to adjust the support width is provided. Depending on requirements, guide plates of varying width or a varying number of guide loops are used. Furthermore, it is known to provide guide plates or guide loops whose support width can be adjusted and that lie in an overlapped manner or are configured to be telescopic. Such constructions are complicated and susceptible to contamination.